It is desirable for the interior of many enclosures, such as electronic enclosures containing disk drives, to be maintained at a controlled humidity. Maintaining a controlled low humidity can have the benefit of avoiding corrosion and deterioration of the electronic components. Similarly, it is often desirable to control the humidity within certain ranges, even when the humidity is not necessarily minimized. For example, in the case of disk drive enclosures, the amount of water vapor within the disk drive enclosure will affect air density, thereby impacting the fly height of read-write heads. In these situations it is desirable to keep a controlled, consistent humidity so that the read-write head height can be kept within specific narrow ranges.
It is possible to place an adsorbent material inside an electronic enclosure to absorb ambient moisture. Silica gel is a particularly common adsorbent for this purpose. Even activated carbon has considerable water adsorbing properties. However, the mere addition of an adsorbent into a disk drive enclosure does not necessarily solve all the water control problems, because the manner in which the water is adsorbed and desorbed during the production, storage, and operation of the disk drive. Specifically, the challenge of controlling humidity within disk drives is compounded by the variable conditions in which electronic enclosures are manufactured and used: disk drive enclosures are often assembled in an open environment where the interior of the drive enclosure, including any adsorbent that is present, can readily absorb atmospheric moisture. It can be appreciated that by limiting the water uptake from the manufacturing environment we can preserve the water capacity for when the disk drive enclosure is subsequently completely or nearly completely sealed.
In some situations the moisture that accumulates within the adsorbent will be released into the sealed (or nearly sealed) electronic enclosure when the disk drive is turned on and heated up, causing an increase in absolute humidity that can influence read-write head fly heights. Other examples of the varying conditions experienced by hard disk drives include exposure to a wide range of environments, such as tropical to temperate to even arctic, as well as operating conditions ranging from frequent on-off cycles of notebook computer drives to constant-on use of server drives. All of these environments and operating conditions can cause disruptions in performance if water content within the drive enclosure is not properly managed.
Therefore, a need exists for the ability to control moisture within electronic enclosures, in particular the ability to control moisture within disk drive enclosures.